After being fired, opportunistic newspaper columnist Anne Mitchell (played by Barbara Stanwyck) pens a fake letter by “John Doe,” who threatens to commit suicide over the injustices experienced by the “common man.” The letter strikes a chord with readers and saves Mitchell’s job. To maintain the ruse, she pays Long John Willoughby (Gary Cooper), a down-on-his-luck former baseball player, to pose as her fictional creation. As John Doe becomes a populist hero, Willoughby is increasingly manipulated by Mitchell and her ambitious boss, D.B. Norton (Edward Arnold), who hopes to use John Doe to further his own political ambitions. When Willoughby eventually tries to reveal the truth, Norton undermines his efforts. Despondent, Willoughby decides to commit suicide but is persuaded not to by John Doe followers.

Cooper won rave reviews as the slow-witted but ultimately honest man who, in classic Capra tradition, manages to overcome the forces of corporate greed and corruption. Capra was forced by the studio to cut his original ending, in which Willoughby commits suicide on Christmas Eve, to make the movie more palatable and uplifting.